1. Field of the Invention
This invention relates generally to latching mechanisms associated with tag axles for vehicles and, more particularly, to a latching mechanism for latching a tailgate mounted tag axle to a vehicle frame.
2. Discussion of the Related Art
Auxiliary axle assemblies or tag axles augment the load carrying capabilities of load hauling vehicles. Tag axle assemblies carry wheels which may be deployed to a ground engaging position or raised to a stowed position. In the ground engaging position, a tag axle system provides an additional supporting axle to redistribute the weight carried by the vehicle among the axles. This additional axle can be employed to increase the weight carrying capability of the vehicle and yet keep it within a per axle legal weight restriction imposed by the state or federal government. In some types of vehicles, such as rear discharging refuse trucks, a rearward directed load distribution predominates and it is advantageous to provide tag axle support as far rearward as possible.
Rear mounted tag axle systems may be attached to the frame or chassis of a vehicle or in a rear discharge vehicle, even to the tailgate. In some applications, a conventional frame mounted tag axle system would interfere with rearward unloading operations. To overcome this difficulty, the tag axle may be carried by or suspended from the tailgate so as to swing up and out of the way with the tailgate when the vehicle unloads. However, conventional tailgate hinges and latches are not built to carry the weight of or withstand the truck supporting forces associated with a ground engaging tag axle system and may pop open or fail during use.
Examples of tailgate hinges and latches may be found in U.S. Pat. Nos. 4,307,541, 3,440,763 and 3,272,552 which describe tailgate latching mechanisms including a latch or pin connected to a pivoting mechanical linkage which is, in turn, attached to a corresponding hydraulic cylinder. As the cylinder is operated, the linkage pivots to open or close the tailgate latch. The tailgate pivots open or closed from hinges situated at the top of the vehicle body.
More examples can be found in U.S. Pat. Nos. 5,141,280, 3,873,149 and 3,757,969 which describe tailgate latching mechanisms wherein the tailgate is hung from vertically displaceable hinges. In each of these patents, hydraulic cylinders lift the tailgate vertically from a closed and latched position before swinging the tailgate open.
Similarly, in U.S. Pat. No. 5,335,958, issued to Christenson (the inventor in this application) et al and commonly assigned with the present invention, hydraulic cylinders raise the tailgate to unlock interlocking side latches before swinging the tailgate open. The latching mechanism described includes a pair of self-aligned vertical stops to prevent vertical displacement of the tailgate when closed. The vertical stops are automatically disengaged as the hydraulic cylinders extend to open the tailgate.
There remains however a need in the art to provide a tailgate mounted tag axle system that does not require the tailgate to carry the full supporting force associated with a deployed tag axle system. Such a system would preserve the advantage associated with a tailgate mounted system while eliminating the drawback associated with supporting forces.